1. Field of Invention
The present invention relates to a light emitting device, especially to an alternating current (AC) light emitting device.
2. Description of Related Art
Light emitting diode (LED) is a light emitting element made of semiconductor material. The light source includes two electrodes. After being applied with voltage (minimum current), the electron-hole recombination process produces some photons due to energy gap of electrons and electron-holes. Thus the LED emits light. The LED is different from a general Incandescent bulb and it's a cold illuminant with features of low power consumption, long lifetime, no idle time, and fast reaction. Moreover, the LED has compact volume, good shock resistance, and suitableness for mass production. Thus the LED is easily to be produced in the form mini-type or array-type element according to users' requirements. It has been applied to electrical appliances, computers and communication products and has become one of the essentials in our daily lives. Generally, a power source is an alternative current (AC). In use, the AC supply should be converted into DC voltage before being applied to semiconductor optoelectronics. Thus an AC to DC converter is added into a driving circuit of semiconductor optoelectronics. Therefore, the cost is increased. Moreover, during the process the AC being converted into the DC, the operational efficiency of the semiconductor optoelectronics is reduced due to power loss. Thus there is a need to develop semiconductor optoelectronics driven directly by an AC supply such as AC light emitting devices with a plurality of light emitting units.
Refer from FIG. 1A & FIG. 1B, a schematic diagram and a circuit diagram of a conventional alternating current (AC) light emitting device are disclosed. The conventional AC light emitting device 10 consists of a substrate 12, a first lighting module 14 and a second lighting module 16. The substrate 12 is disposed with a first electrode 122 and a second electrode 124. The first lighting module 14 as well as the second lighting module 16 is also arranged on the substrate 12. The first lighting module 14 and the second lighting module 16 are respectively coupled to the first electrode 122 and the second electrode 124. The first lighting module 14 includes a plurality of first light emitting units 142 that are electrically connected in series by a first conductor 144. The second lighting module 16 includes a plurality of second light emitting units 162 that are electrically connected in series by a second conductor 164. The total area of the multiple first light emitting units 142 is the same with that of the multiple second light emitting units 162. But electrical properties of the series connection of the first light emitting units 142 are different from electrical properties of the series connection of the second light emitting units 162. The simplified circuit diagram of the conventional AC light emitting device 10 is shown in FIG. 1B. The electrical properties of series connection of the first lighting module 14 and those of the second lighting module 16 are opposite and they are coupling in an AC power source 18. By opposite electrical properties of series connection of the first lighting module 14 and of the second lighting module 16, the first light emitting units 142 of the first lighting module 14 and the second light emitting units 162 of the second lighting module 16 emit light in turns within a positive and a negative half-wave cycle of the applied power source 18.
However, the plurality of first light emitting units 142 of the first lighting module 14 and the plurality of second light emitting units 162 of the second lighting module 16 respectively occupy half of the area of the substrate 12. Thus within the wave cycle of an AC power, the lighting area of the conventional AC light emitting device 10 is only half of the total area. Thus the lighting efficiency provided by lighting area of the first lighting module 14 and that of the second lighting module 16 of the conventional AC light emitting device 10 is only half of original light emitting efficiency. Moreover, within the plurality of first light emitting units 142 and the plurality of second light emitting units 162 of the AC light emitting device 10, the light emitting unit is electrically coupled to an adjacent light emitting unit by one conductor 144, 164. Thus once one of the conductors 144, 164 is broken, an open circuit occurs in one of the first lighting module 14 and the second lighting module 16 of the conventional AC light emitting device 10 so that the lighting module will not emit light. Therefore, the conventional AC light emitting device 10 only works during a positive or a negative half-wave cycle.
In order to solve above problem of lighting area, a light emitting device is disclosed in Pub. No.:WO2007083885 “LIGHT EMITTING DEVICE WITH LIGHT EMITTING CELLS ARRAYED” applied by Mr. LEE, Jae-Ho. The light emitting device comprises a substrate, a light emitting cell block, and a bridge rectifying circuit. The light emitting cell block and the bridge rectifying circuit are disposed on the substrate. The bridge rectifying circuit is arrayed to surround the light emitting cell block while the bridge rectifying circuit includes a plurality of diodes and the light emitting cell block consists of a plurality of light emitting cells. The plurality of light emitting cells is electrically coupled in series by a wire. The bridge rectifying circuit is provided on the substrate surrounding a peripheral portion of the light emitting cell block, occupying surrounding area of the substrate. Thus the bridge rectifying circuit reduced effective lighting area of the device. The diodes area electrically connected in series by a wire. Thus if one of the wires is broken, an open circuit occurs in one of the bridge rectifying circuit and the light emitting cell block. Therefore, the bridge rectifying circuit and the light emitting cell block will have a breakdown.
In order to solve above problems, there is a need to invent a new AC light emitting device that increases effective lighting area for improving light emitting efficiency by disposition of light emitting units with various area on the substrate. Moreover, the adjacent light emitting units of a plurality of light emitting units are coupled with each other by a plurality of wires.